JPH10167856A - Porous ceramic and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To steadily produce high-strength porous ceramic. SOLUTION: Water is absorbed in fine particles of a water-swellable water- absorbing resin having >=10,000dyn/cm<2> gel strength to form gel. This gel is mixed with ceramic powder and compacted. The resultant compact is fired to obtain the objective porous ceramic having >=40% porosity and bending strength corresponding to >=15% of that of dense ceramic made of the same material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a porous ceramic and a method for producing the same. This method is suitable for producing a porous ceramic used for a sensor element, a catalyst carrier, a non-combustible building material, a heat insulating material, a soundproofing material, a shock absorber and the like.

[0002]

2. Description of the Related Art Conventionally, as a method for producing a porous ceramic, (a) a method of using a light-weight substance whose skeleton itself such as vermiculite or pearlite is porous, and (b) a method of adding a foaming agent to a ceramic raw material. And (c) a method of mixing a water-absorbent resin with a ceramic raw material is known. In each case, after the raw material powder is formed into a predetermined shape, it is fired in a furnace to obtain a porous ceramic as a sintered body.

[0003] Of these methods, (a) is limited by the type of raw material, and (b) is difficult to stabilize the porosity and pore size, so that products of the same quality cannot be stably obtained. (C) has been proposed as an improvement method free from such problems (Japanese Patent Laid-Open No.
-47775, JP-A-62-212274, JP-A-62-222674).

[0004]

However, the conventional method (c) has a problem in that the molded body is deformed after the molding and before the firing is completed, and the strength of the product is low. Therefore, an object of the present invention is to provide a method capable of stably producing a high-strength porous ceramic.

[0005]

In order to achieve the object, a method for producing a porous ceramic according to the present invention is directed to a method for producing fine particles of a water-swellable water-absorbent resin having a gel strength of 10,000 dynes / cm ² or more. A step of forming a gel by absorbing water, a step of mixing and molding the gel and ceramic powder that have absorbed water,
And firing the molded body. According to this method, a porous ceramic having a porosity of 40% or more and a bending strength of 15% or more of the bending strength of the dense ceramic made of the same component can be obtained.

[0006]

According to the present invention, in molding the ceramic powder,
A water-absorbing gel of water-swellable water-absorbent resin fine particles is added to the ceramic powder in advance. The water-absorbing gel of the water-swellable water-absorbing resin has a sticky surface. Moreover, since the water-absorbing resin is fine particles, the water-absorbing gel has a viscosity like glue. For this reason, even if the raw material is not sticky even when kneaded with water, the tackiness and viscosity of the water-absorbing gel acts, and when kneaded, stickiness and plasticity are imparted, and the moldability is improved.

The water-absorbing gel of the water-absorbing resin particles is
Unlike a water-soluble resin, it has a function of retaining water inside the gelled particles by absorbing water. That is,
Even if the water content after molding is the same, much water is swelled in this water and is taken into the water-absorbing gel which does not dissolve in water.

[0008] Since the water-absorbing gel takes in water as described above, the amount of water existing in the gaps between the raw material particles is small even if the water content of the molded body is in the same range as the conventional one. In addition, the gel which governs the mechanical strength of the molded product has a strength of 10,000
0 dyne / cm ² or more. Therefore, the compact has sufficient rigidity and does not deform until it is sintered.
Preferred gel strength is 15,000 to 50,000 dynes / cm ² . Since the strength of the molded body is high, the mixing ratio of the (water-absorbed gel / ceramic powder) is 0.2% by weight.
It can be selected from a wide range of ~ 2.4. However, in order to obtain the above porous ceramic, the mixing ratio is 0.6.
The above is preferred.

In the present invention, the gel strength is a value obtained by measuring by the following method. <Measurement method of gel strength>
g / g of a water-absorbent resin, a water-absorbent gel obtained by absorbing M × 0.75 g of physiological saline in 1 g of a water-absorbent resin is applied with a load of 200 g through a 3 mm-diameter disc at room temperature. Rebound stress when applied at a descent speed of 0.36 cm / sec.

Further, the water-swellable water-absorbent resin fine particles swell in a gel state with water absorption but do not dissolve in water.
It will be scattered in the form of independent particles in the compact. Therefore, it is considered that the portion having the water-absorbing gel particles after firing becomes independent pores, and the ceramic obtained after firing has a high strength despite being porous. And since it is porous, it is also possible to reduce the weight of the ceramic while maintaining the physical properties such as the strength of the conventional ceramic.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The water-swellable water-absorbing resin preferably has the following properties such as water-absorbing performance, average particle size and gel strength.

First, the water absorption performance with respect to pure water is 50 g /
g or more, preferably 100 to 1,000 g / g. If the water absorption performance is lower than 50 g / g, the shape retention of the molded article is insufficient. The water-swellable water-absorbing resin is in the form of powder or granules, and has an average particle size of 1000 microns or less, preferably 5 to 550 microns. If the average particle size is larger than 1000 microns, the shape retention of the molded product is insufficient.

The water-swellable water-absorbing resin satisfying the above physical properties becomes water-soluble by, for example, starch or cellulose and a water-soluble monomer containing a hydrophilic group such as a carboxyl group or a sulfonic acid group and / or by hydrolysis. Monomers and
It can be obtained by polymerizing a crosslinking agent as an essential component and, if necessary, performing hydrolysis. The production method and specific examples of this water-absorbent resin are described in JP-A-52-25886 and JP-B-53-1983.
-46199, JP-B-53-46200 and JP-B-55-21041.

Other examples of the water-swellable water-absorbing resin include a hydrolyzate of a starch-acrylonitrile graft polymer, a hydrolyzate of a cellulose-acrylonitrile graft polymer, a cross-linked product of carboxymethyl cellulose, and a partially hydrolyzed polyacrylamide. Decomposition products, cross-linked acrylic acid-acrylamide copolymers, cross-linked sulfonated polystyrene, vinyl ester-unsaturated carboxylic acid copolymers disclosed in JP-A-52-14689 and JP-A-52-27455. Saponified polymer, cross-linked polyacrylic acid (salt), cross-linked acrylic acid-acrylate copolymer, cross-linked isobutylene-maleic anhydride copolymer and cross-linked carboxylic acid-modified polyvinyl alcohol, Crosslinkable polyacrylates and the like can be mentioned. Further, two or more of the above-described water-absorbing resins may be used in combination.

In the present invention, the water-absorbing gel is obtained by adding water to the fine particles of the water-absorbing resin described above, and the swelling ratio is not particularly limited. It is preferable to use a saturated state (saturated water absorbing gel).

The molding aid composed of a water-absorbing gel is used together with a ceramic raw material such as clay in the ceramic molding process. As the ceramic raw material, clay or plastic ceramic powder which is conventionally suitable for ceramic production is of course used. It is possible to use non-plastic or low-plastic materials which are not suitable for ceramic production, either alone or in combination with plastic materials. Examples of such ceramic materials include the following.

(1) Plastic raw materials: Clay minerals such as kaolin, laurite, bentonite, pottery stone, etc. (2) Non-plastic or low-plastic ceramic raw materials: Alumina, titania, Frog-eye clay once dried and pulverized,
Silica sand, magnesite, magnesium silicate, pulverized material including waste products of general ceramics products, waste incineration ash

EXAMPLES In each of the following examples, the evaluation criteria are as follows.

[Gel Strength] The saturated liquid absorption (Mg / g) of the water-absorbent resin with respect to physiological saline was measured in advance by the tea bag method (JIS K7223-1996). (M × 0.75)
g of physiological saline in a 100 cc beaker, 600
1 g of the water-absorbing resin (60 to 100
(Mesh) to uniformly absorb the water, thereby producing a water-absorbing gel having a smooth surface. This water-absorbing gel was kept at 25 ° C., and under the following conditions, a neo card meter (M3, manufactured by Iio Electric Co., Ltd.)
(Type 02) was used to measure the gel strength. Load: 200 g Diameter of pressure-sensitive shaft: 3 mmφ Descent speed of pressure-sensitive shaft: 0.36 cm / sec

[Bending Elasticity of Molded Body] Loads of various sizes with a span of 20 cm were applied to the molded body after extrusion by a kneader and before drying, and the maximum displacement in the vertical direction after a load of 30 seconds was measured. This displacement depends on the shape retention of the molded body. [Bending strength of formed body and fired body] The bending strength of the formed body or fired body was measured in accordance with JIS R1601.

Example 1 As water-swellable water-absorbent resin fine particles, an average particle diameter of 100 μm was used.
m, water absorption capacity 400 g / g, gel strength of 20,000 dynes / cm ² , crosslinked starch-acrylic acid graft resin (Sunwet IM-2 manufactured by Sanyo Chemical Industries, Ltd.)
800D) was prepared. The average particle size of the resin was adjusted by passing it through a sieve after grinding. 370 g of water was absorbed per 1 g of the resin to form a water-absorbing gel.

An alumina powder having an average particle size of 0.5 μm and a purity of 99% was prepared as a ceramic raw material. In a vacuum kneader, 1680 g of this ceramic material and 1850 of water-absorbing gel were added.
g and kneaded. The amount of the resin component is 0.05 part by weight based on 100 parts by weight of the inorganic substance in the kneaded material. The kneaded material was placed in an extruder equipped with a die having a cross section of 4 cm × 2 cm, and extruded at a speed of 40 cm / min to obtain a molded body having a size of 4 × 2 × 25 cm. This molded product was prepared as Sample No. Let it be 1. The water content of the molded body is calculated to be 52%. The bending elasticity and the bending strength of this molded body were measured.

Next, the molded body is air-dried, and the moisture content is 12%.
From the time when the temperature was lowered to 50 ° C., the resultant was placed in an electric furnace and dried by heating at 50 ° C., and then the molded body was fired in the air at a temperature of 1500 ° C. The bulk specific gravity, porosity, thermal conductivity, and bending strength of the fired body were measured. In parallel, instead of adding the water-absorbing resin, a small amount of an organic binder was added, and the mixture was molded under pressure and fired under the same conditions to obtain a fired body having a relative density of 99.5%.

Example 2 Water-swellable water-absorbent resin fine particles having an average particle diameter of 100 μm
m, water absorption capacity 400 g / g, gel strength 30,000 dynes / cm ² , except that it is a cross-linked polyacrylic resin (pulverized product of Sanfresh ST-500D manufactured by Sanyo Chemical Industry Co., Ltd.). And a fired body were obtained under the same conditions as in Example 1. Sample No. of the compact and the fired body Is set to 2.

Example 3 Water-swellable water-absorbent resin fine particles having an average particle diameter of 100 μm
m, water absorption capacity 320 g / g, gel strength 50,000 dynes / cm ² Crosslinked acrylic resin (3 parts of a 5% aqueous solution of ethylene glycol diglycidyl ether are sprayed into 100 parts of the above-mentioned Sun Fresh ST-500D and permeated. And then dried at 150 ° C.) to obtain a molded body and a fired body under the same conditions as in Example 1. Sample No. of the compact and the fired body
Is set to 3.

Comparative Example 1 The water-swellable water-absorbent resin fine particles had an average particle diameter of 100 μm.
m, water absorption performance 900 g / g, gel strength 9,000 dynes / cm ^2, a crosslinked starch-acrylic acid graft resin (Sunfresh ST-1 manufactured by Sanyo Chemical Industry Co., Ltd.)
A molded product and a fired product were obtained under the same conditions as in Example 1 except that the same material as in Example 1 was used except for the case of (00). Sample No. of the compact and the fired body Is R1.

Example 4 A molded body and a fired body were obtained under the same conditions as in Example 2, except that the amount of water per gram of resin was 420 g and the water content of the molded body was calculated to be 56%. . Sample No. of the compact and the fired body Is set to 4. Comparative Example 2 A molded body and a fired body were obtained under the same conditions as in Comparative Example 1 except that the amount of water per 1 g of resin was 420 g and the water content of the molded body was 56% in calculation. Sample No. of the compact and the fired body Is R2.

Example 5 A molded product and a fired product were obtained under the same conditions as in Example 2 except that the amount of the resin component was changed to 0.1 part by weight based on 100 parts by weight of the inorganic substance in the kneaded material. Sample No. of the compact and the fired body Is set to 5. Comparative Example 3 A molded body and a fired body were obtained under the same conditions as in Comparative Example 1 except that the amount of the resin component was changed to 0.1 part by weight based on 100 parts by weight of the inorganic substance in the kneaded material. Sample No. of the compact and the fired body Is R3.

Example 6 Water-swellable water-absorbent resin fine particles having an average particle diameter of 500 μm
A molded body and a fired body were obtained under the same conditions as in Example 2 except that they were the same as in Example 2. Sample No. of the compact and the fired body Is set to 6. Table 1 shows the production conditions and measured physical properties of the molded and fired bodies obtained in the above Examples and Comparative Examples.
And Table 2.

[0029]

[Table 1]

[0030]

[Table 2]

[0031]

According to the present invention, a high-strength porous ceramic can be stably obtained without being limited by the type of ceramic raw material.

Claims (6)

[Claims] 1. A porous ceramic having a porosity of 40% or more and a bending strength of 15% or more of the bending strength of a dense ceramic comprising the same component. 2. A process in which water is absorbed into fine particles of a water-swellable water-absorbent resin having a gel strength of 10,000 dynes / cm ² or more to form a gel, and a process in which the gel and ceramic powder mixed with water are mixed and molded. And a step of firing the formed body. 3. Mixing ratio (water-absorbed gel / ceramic powder)
Is from 0.2 to 2.4 on a weight basis. 4. The method for producing a porous ceramic according to claim 2, wherein the water-swellable water-absorbent resin has a water absorption performance of 100 to 1,000 g / g with respect to pure water. 5. The method for producing a porous ceramic according to claim 2, wherein the average particle diameter of the water-swellable water-absorbent resin fine particles is 5 to 550 μm. 6. The method for producing a porous ceramic according to claim 2, wherein the water-swellable water-absorbent resin fine particles are converted into a saturated water-absorbent gel in the gelling step.